All yarns of synthetic fibers, including yarns of polyester fibers, can be classified into two groups, namely (1) continuous filament yarns and (2) spun yarns, meaning yarns of fibers that are discontinuous, which latter fibers are often referred to as staple fibers or cut fibers. This invention provides improvements developed primarily in relation to the latter group of polyester fibers, but such polyester (staple) fibers have first been formed by extrusion into continuous polyester filaments, which are processed in the form of a tow of continuous polyester filaments.
The terms "fiber" and "filament" are often used herein inclusively, without intending that use of one term should exclude the other.
This invention was developed primarily to solve problems encountered in relation to tows of continuous polyester filaments as it has been desirable to provide a capability of better processing downstream on the worsted system than has existed for polyester tows that have been available commercially heretofore. As will be seen hereinafter, the solution I have provided to the problems that I have encountered is a new polyester filament of unique cross-section that is conveniently referred to often herein as "scalloped-oval" or "hexachannel scalloped-oval." My new polyester filaments have also shown advantages in other applications.
Mostly, the objective of synthetic fiber producers has been to replicate advantageous properties of natural fibers, the most common of which have been cotton and wool fibers. Most commercial polyester cut fiber has heretofore been blended with cotton. A typical spun textile yarn contains about 140 fibers of 1.5 dpf (denier per filament, explained hereinafter) and 1.5 inch length in its cross-section (of cotton count 25). Polyester worsted yarns are different, with fibers that have been of 4 dpf and 3.5 inch length, typically being of worsted count 23, and of cross-section containing about 60 fibers for single yarn and about 42 fibers for bi-ply yarn; the denier and length may vary up to about 4.5 and down to about 3, and the yarn count may vary over 55 worsted to 10 worsted. It is only relatively recently that the advantages of using synthetic fibers of dpf lower than the corresponding natural fibers (such as wool) have been found practical and/or been recognized. Recent attempts to provide low dpf polyester fiber for blending with wool on the worsted system have not, however, been successful, and require improvement. As the fiber denier has been reduced, the fibers have become harder to process (carding, drafting, gilling, etc.) in the mill. In fact, below a certain fiber denier, the commercially-available polyester fibers that I have tried have been practically impossible to process on the worsted system, and/or have given poor quality fabrics. Thus, for commercially-acceptable processing and blending with wool in practice, I have found that the fiber denier of such polyester fibers has had to be a minimum of about 3 dpf. Tows of (nominal) dpf less than 3 are not believed available commercially at this time. This has been the status so far in the trade. Thus far, trying to manipulate a desire to reduce dpf has appeared to be contradictory or incompatible with satisfactory mill processibility.
Processing on the worsted system is entirely different from most practice currently carried out on the cotton system, which generally uses cotton fiber that is sold in bales and that may be mixed with polyester fiber that is primarily staple or cut fiber, that is also sold in compacted bales. In contrast, for processing on their system, worsted operators want to buy a tow of polyester fiber (instead of a compacted bale of cut fiber) so they can convert the tow (which is continuous) into a continuous sliver (a continuous end of discontinuous fibers, referred to hereinafter shortly as "cut fiber") by crush cutting or stretch-breaking. This sliver is then processed (as a continuous end) through several stages, i.e., drafting, dyeing, back-washing, gilling, pin-drafting and, generally, finally blending with wool. It is very important, when processing on the worsted system, to maintain the continuity of the sliver. Also, however, it is important to be able to treat the cut fiber in the sliver appropriately while maintaining a reasonably satisfactory processing speed for the continuous sliver. As indicated, recent attempts to use desirable polyester tow, e.g., with low dpf, have not produced desired results. For instance, unsatisfactorily low machine productivity rates have been required after dyeing; I believe this may have been because such polyester fiber has previously packed together too tightly.